Question

give short answers:

24) Describe how oxygen and carbondioxide are transported in the blood.

25) Describe the mechanisms responsible for haemostasis.

26) Discuss the determinants of vascular resistance.

27) Write an essay on the exchange function of blood capillaries.

Answer 1

24. The blood contains dissolved gases in it. Oxygen and cardon dioxide are the main gases dissolved in blood.
When the oxygen rich inspired air reaches the lungs, the oxygen is diffused theough the alveolar membrane into the blood and the impure blood containing high amount of CO2 diffuses into the alveoli and is expelled put of the body through expiration. The oxygen in the blood binds to the hemoglobin and is transported to body tissues and cells. Cells contain high amount of CO2 then blood because of various metabolic processes. When the blood rich in oxygen reaches the cell the carbon dioxide moves to the blood and oxygen is taken up by the cell by the process of diffusion. Hemphlobin has higher affinity for CO2 compared to oxygen and releases the oxygen and binds to CO2. The CO2 is then carried by the blood to the lungs where it is expelled out.
25. Homeostasis is the maintenance of a constant internal body environment by regulating the ph, blood pressure, temperature, blood osmolality in a narrow physiological range. Any deviation in the internal body environment leads to imbalance in body. A homeostatic loop helps to maintain this constant environment. It consists of a receptor which gets stimulated due to change in controlled variable. The receptor sends sensory afferent impulses to the integrating centre. The integrating centre sends motor impulses to the effector organ which alters its activity or release substances or hormones that act on different organs, hlands or muscle to alter the activity and restore the balance. Homeostatic loop may be positive feedback or negative feedback.
26. Vascular resistance is the resistance offered by the walls of vessels to the blood flowing through them. It depends on following factors:

1. blood viscosity : increase in blood viscosity increases vascular resistance.
2. Vessel diameter  : decreased lumen of the blood vessel such as during vasoconstriction increases the vascular resistance

3. Vessel length : the increase in vessel length increases the vascular resistance.
27. Capillaries are small diameter blood vessels connecting the arterioles and venules. Capillaries are the main site of exchange of substances between the blood and surrounding interstitial fluid. Capillary walls are very thin and allow exchange of substances through it such as water, ions, glucose and gases.
The exchange of gases depends upon the starling forces. At the arterial end capillary hydrostatic pressure is higher than blood colloidal osmotic pressure resulting in fluid and substances moving out of the capillary. As the blood flows and reaches the middle of capillaries the capillary hydrostatic pressure equals blood colloidal osmotic pressure and there is no movement of fluid in or out of capillary. At the venous end capillary hydrostatic pressure decreases and becomes less than blood colloidal osmotic pressure. This causes entery of fluid into the capillary.